The establishment of a number of cultured cell lines of retinoblastoma during the past several years has opened the way for a new program of research with this malignancy. It has made possible a short-term, but effective and dependable, ocular model of the disease in immunosuppressed rabbits. Various retinoblastoma cell lines will be studied in vitro and in our animal model for the range of cellular sensitivity to the photodynamic activity of natural and synthetic porphyrins such as hematoporphyrin and tetraphenylporphine sulfonate. Retinoblastoma karyology of the tumor, and of family member lymphocytes, will be examined for possible distinguishing chromosome abnormalities. Cell lines will be used in animal studies to determine their ability to develop metastatic spread. They will also be examined for antigenic and biochemical characteristics that may help establish the cell of origin in the retina.